The present invention relates generally to the application of liquid material to elongated material and more particularly to a method for coating or impregnating strands of material, for example glass fiber strands, with liquid resin.
As will be seen hereinafter, the present invention is directed specifically to the "wetting out" or impregnation of glass fiber strands with liquid resin in the manufacture of glass reinforced plastic pipe. There are however numerous manufacturing operations which require applying a liquid, for example liquid resin, to elongated material, for example glass fibers either in strand or single element form. As a result, there are numerous wet out or impregnation techniques in the prior art.
One typical resin impregnating technique calls for passing the material to be impregnated directly through a bath of resin. There have been several different ways to accomplish this. One method, which has been referred to as the "funnel and plug" method calls for moving the material, for example the glass filaments or strands, into a funnel filled with resin and out through the bottom of the funnel past a plug. Another method calls for dipping the fibers or filaments into and out of a bath of resin utilizing dip rollers to guide the fibers.
While the funnel and plug method is uncomplicated in that it requires few if any moving components in the resin bath itself, this method has several disadvantages. For example, it is difficult to control wet out or resin impregnation and generally more than the desired amount of resin is placed on the fibers or filaments. The dip method using rollers in the bath itself also has many disadvantages. One major disadvantage using this method is that it is quite difficult to thread the fibers or filaments, either initially or after a break. In addition, in the event one or more fibers or filaments break during operation, these broken fibers have the tendency to wrap around the moving rolls. This "roll wrap" problem as it is commonly referred to can result in the entire resin impregnating system being shut down for relatively long periods of time.
Another and probably more commonly used method of applying resins to fibers may be referred to as the "transfer" technique. In accordance with this technique generally, one or more rollers are used to transfer resin from a bath to the fibers. Either the resin is transferred directly from one roller onto the moving fibers in contact with the roller or it is transferred via a series of rollers and ultimately onto the moving fibers in contact with the last roller in the chain. There are a number of specific techniques of this general type as exemplified by the following patents:
U.s. pat. No. 2,728,972 PA0 U.s. pat. No. 2,873,718 PA0 U.s. pat. No. 2,968,278 PA0 U.s. pat. No. 2,157,212 PA0 U.s. pat. No. 3,244,143 PA0 U.s. pat. No. 2,118,517 PA0 U.s. pat. No. 3,082,734 PA0 U.s. pat. No. 2,868,162 PA0 British Pat. No. 1,273,377 PA0 Canadian Pat. No. 712,090
In all of these patents, the material being coated or impregnated moves into contact with a moving surface, in most cases a moving drum or roller. This moving surface, for example the drum, transfers the liquid coating onto the moving material to be coated or impregnated. There are a number of drawbacks with this general transfer method and the many specific transfer methods disclosed in the prior art. One major disadvantage is that it is highly susceptible to the roll wrap problem discussed above.
As will be seen hereinafter, the present invention, in its preferred embodiment, it also directed to wetting out or impregnating fibrous material, particularly glass fiber strands, with liquid resin. However, as will also be seen hereinafter, the manner in which this is accomplished is entirely different than the methods discussed above and does not have many of the drawbacks associated with these prior art methods.